East Herts Borough Council have reviewed their Green Belt policy and permitted two new housing developments adjacent to the park. The first of these, named Blakemore Manor by the developer, is well underway with some of the new homes occupied already, more here. As far as we know there never was a Blakemore Manor in this part of Hertfordshire, the name lends an air of distinction to the development presumably. Welwyn Hatfield Borough Council intends to permit large housing developments to the west of the park, on previously undeveloped land, much of it in the green belt.
Here is the Green Belt buffer around the park prior to any changes, also shown is where the new housing developments are being planned for. The 250 home site is the Blakemore Manor site currently well underway.
Potential new nearby housing numbers by 2030, assuming that they all go ahead.